The aspects of the disclosed embodiments relate to a valve, the operation of which is provided by a remotely controlled actuator. More particularly, the disclosed embodiments relate to a device and to a method for detecting failures in the main constituent elements of a valve, such as a drive shaft or a motor of the valve, especially when the valve is used in an circuit which is important for safety reasons, such as an aircraft fuel circuit.
Aircraft fuel circuits generally include fuel valves for performing functions such as cutting off the feed to the engines, opening for refueling or transferring fuel between independent tanks.
As illustrated in FIG. 1, a fuel valve 1 comprises an actuator 11 driven by an electric motor 12 coupled to a reduction gear. The actuator 11 rotates a spherical ball 13 by means of a drive shaft 14 which penetrates into a fuel tank 15. The spherical ball 13 is inserted into a valve body 16 and is mounted so as to rotate as one around an axis 132 inside said valve body. The spherical ball 13 has a through-opening 133 of axis 134, approximately perpendicular to the axis 132. The valve body 16 has two approximately cylindrical ends 161, of diameter substantially smaller than the diameter of the spherical ball, to which ends fuel flow pipes 17 are fixed. The two ends 161 of axis 171 are substantially aligned, approximately perpendicular to the axis 132.
In such a fuel valve, there is no intermediate position in normal operation, the valve either being in an open position or in a closed position.
When the valve is in an open position, to allow fuel to flow, the axis 134 of the opening 133 of the spherical ball 13 and the axis 171 of the flow pipes 17 are substantially coaxial.
When the valve is in a closed position, to block the flow of fuel, the axis 134 of the opening 133 of the spherical ball 13 and the axis 171 of the flow pipes 17 are substantially perpendicular.
The current methods for monitoring such valves consist in comparing the controlled position of the valve and the detected position of the valve by means of switches positioned in the actuator 11. A fault in the monitoring devices is associated with the risk of one or more switches failing, for example due to electrical contact problems or to damage to the mechanism of the switch. In this case, the position of the valve cannot be determined and an error message, such as for example “unknown failure” is returned to a system for monitoring the aircraft. A maintenance operation is then necessary to close the valve in a known position and to replace the actuator 11, which may entail taking the aircraft out of service and may require relatively long times for detecting and executing the failure. Another limitation lies in the fact that only the position of the actuator 11 is monitored, and not the actual position of the spherical ball 13 or that of the drive shaft 14. This limitation leads to the possibility of hidden failures. Thus, it is possible for the position of the actuator 11 to be detected and sent to the flight deck although the spherical ball 13 is not in the corresponding position, for example following an undetected fault of the drive shaft 11. Such hidden failures, among them the failure of the drive shaft 11, are liable to affect the operational availability of an aircraft and it is necessary to program maintenance operations at regular intervals to check that the valves are operating correctly, which may prove to be penalizing for airlines.
One solution consists in adding position sensors on the spherical ball 13. However, the use of such sensors would involve introducing cables into the fuel tank, and this may lead to risks of short circuits.
Patent applications US 2003/193310 and US 2005/156550 and Japanese patents JP 7280705 and JP 1121733 and Japanese patent application JP 19930349329 describe various devices using dedicated microprocessors coupled to position sensors placed either actually inside the motor or on or adjacent to the drive shaft 14. Such solutions prove to be complex and have the drawback of increasing the number of sensors and in particular their associated power supplies close to the fuel tank.